knudsen (11/23/82)
I beg to differ with two points of recent 6502 discussion (NOT the HCF, thank Darwin!). First, the 6502 does not read truly "random" addresses on indexed modes; it would read only the address exactly one page (256. bytes) below the desired target. Likewise it might hit an I/O register on the way to an addr 256. bytes higher. The cure is to pack your I/O device regs together in one page and have nothing in the page preceding or following (and decode ALL the high-byte address leads when enabling those regs!). Yeah, that's uncool, but it sure beats "random" peeks. Also, if the highly-touted 6502 prefetches are all discarded, how do you explain the oft-quoted statement that "a 6502 can move a string/array with plain old firmware faster than a Z80 using its block-moves"? Maybe that claim is untrue; but without prefetching by the 6502, it's just plain ridiculous. (Wish I could recall where I last read it). I didn't divorce KIM just to marry COCO (one more way computers are better than women) mike k
msm@sri-unix (11/24/82)
While I haven't seen the Z80 block move timings, I think that they stand a good chance of being slower than those for the 6502. The main reason for this is that the 6502 takes only a single clock cycle to access memory instead of the 8080 family's 3 cycles. Michael S. Maiten Silicon Gulch, California <...!{ucbvax!menlo70,decvax}!sytek!msm>